Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed. Flash memory is primarily used in memory cards and USB flash drives for general storage and transfer of data between computers and other digital products. Flash memory is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory) that is erased and programmed in large blocks. Example applications include storage for PDAs (personal digital assistants), laptop computers, digital audio players, digital cameras and mobile phones. Other applications include game consoles, where flash memory can be used instead of other types of EEPROMs or battery-powered SRAM for game save data.
NAND type flash memory is one of two types of flash memory technologies (the other being NOR) that are currently available. NAND type flash memory is best suited for use in flash devices requiring high capacity data storage. NAND type flash memory provides significantly more storage space, and offers faster erase, write and read capabilities as compared to NOR type flash memory.
FIG. 1 shows a layout representation of a conventional NAND memory cell string 100 that features a conventional select gate structure. In FIG. 1 NAND string 100 has a defined number of wordlines 101 (16, 32, or 64 depending on product design) sandwiched between a “drain select gate” 103 at one end of the string structure and a “source select gate” 105 at the other end of the string structure. As shown in FIG. 1 the distance between a first edge of each wordline and the first edge of the next wordline is 80 nm and the distance between a first edge of each string and a first edge of the next string is 80 nm. Moreover, the width of the select drain gate and the width of select source gate is 200 nm.
Conventional channel engineering design for conventional NAND type memory structures, such as that shown in FIG. 1, provide an obstacle to the scaling down of the sizes of the select gates of such NAND type memory structures. Accordingly, the transistor gate design, including the materials used, of conventional NAND type memory provides an unsatisfactory hindrance to miniaturization efforts for NAND type memory structures.